Investments (Summary Of Amortized Cost And Market Value Of Fixed Maturity Securities, By Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, at market value, Amortized Cost	$ 7,539,624	$ 7,334,425
Fixed maturity securities - available for sale, Market Value	7,496,815	7,492,079
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Due in one year or less, Amortized Cost	617,696	569,506
Fixed maturity securities - available for sale, Due after one year through five years, Amortized Cost	2,878,464	2,919,966
Fixed maturity securities - available for sale, Due after five years through ten years, Amortized Cost	1,626,513	1,541,695
Fixed maturity securities - available for sale, Due after ten years, Amortized Cost	589,138	602,440
Fixed maturity securities - available for sale, Due in one year or less, Market Value	611,935	563,730
Fixed maturity securities - available for sale, Due after one year through five years, Market Value	2,885,401	2,963,903
Fixed maturity securities - available for sale, Due after five years through ten years, Market Value	1,654,400	1,602,642
Fixed maturity securities - available for sale, Due after ten years, Market Value	548,828	620,473
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, at market value, Amortized Cost	875,091	761,607
Fixed maturity securities - available for sale, Market Value	800,118	765,957
Commercial [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, at market value, Amortized Cost	313,624	311,961
Fixed maturity securities - available for sale, Market Value	329,328	329,049
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, at market value, Amortized Cost	638,008	625,612
Fixed maturity securities - available for sale, Market Value	665,728	644,687
Non-agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, at market value, Amortized Cost	1,090	1,638
Fixed maturity securities - available for sale, Market Value	$ 1,077	$ 1,638

Amount of debt securities categorized neither as held-to-maturity nor trading, held at market value.

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